Like this:

Looking at photos of Joe Khachan’s electron gun, it is clear that my electron gun is producing much more coronal discharge:

My electron gun.

Joe's electron gun.

I emailed Joe to get his thoughts on the matter. He replied:

Two reason for the difference with yours could possibly be the following: we operate in hydrogen and we work below 10 mTorr. We have a large chamber which helps in breakdown at lower pressure. Since your chamber is smaller, you may need to operate at a higher pressure but this will reduce the depth of the virtual cathode that can be established. You may be able to reduce the pressure by using electron emission from a light bulb tungsten filament. You’ll need to extract the electrons from the filament by applying a potential difference between the filament and, say, a wire mesh as the anode. The electrons will go through the anode and produce enough ionization to enable you to start the discharge at lower pressure. The lower pressure also produces deeper virtual cathodes within the polywell.

Perhaps we could run this experiment with NO gas… only electrons from a hot cathode? See Vacuum Arc.

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Joe adds:

Yes, just using an electron gun would be the better way to do this. We are making electrons guns based on a hot filament in order to do this. It is possible to get quite a large current from a filament of about an amp. A gun is needed in order to direct the electrons into the polywell because it is made of teflon. Bussard did it with filaments and used the voltage bias on WB6 to draw the electrons into it, so the WB6 is part of the electron gun.